1. Field of the Disclosure
The present disclosure relates to line-of-sight detection apparatuses that can detect a line-of-sight direction of the driver of a vehicle or a target person other than the driver.
2. Description of the Related Art
In the gaze point detection method disclosed in International Publication No. 2012/020760, two cameras are arranged so as to face an eye of a target person. Two types of light source are arranged around each camera in such a manner as to form two concentric circles. Light sources that radiate light having a center wavelength of 850 nm are arranged along the inner circle nearer to the camera and light sources that radiate light having a center frequency of 950 nm are arranged along the outer circle. The camera can obtain a bright pupil image radiating the 850 nm light, and can obtain a dark pupil image by radiating the 950 nm light.
With this gaze point detection method, a pupil image is obtained on the basis of the bright pupil image and dark pupil image, and a cornea reflection point for the light source is obtained from the dark pupil image. On the basis of these images, vectors from the cornea reflection point of the target person to the pupil in planes perpendicular to reference lines connecting the cameras to the cornea are calculated, and the line-of-sight directions of the target person with respect to the reference lines of the respective cameras are calculated on the basis of these vectors by using a predetermined function.
Japanese Unexamined Patent Application Publication No. 2012-55428 discloses an arrangement in which the line-of-sight direction of a target person is detected by using two detection means. The first detection means detects the line-of-sight direction on the basis of the position of a pupil image and the position of the cornea reflection image of the light from a light source. The second detection means detects the line-of-sight direction on the basis of the position of the pupil image and the position of a predetermined portion of a face image that does not include the cornea reflection image. It is stated in the disclosure of Japanese Unexamined Patent Application Publication No. 2012-55428 that, as the function of the second detection means, the line-of-sight direction is detected on the basis of the relationship between the position of an inner eye corner and the position of the pupil image by detecting the position of the inner eye corner by using an inner-eye-corner detection unit.
When the difference between the line-of-sight direction detected by the first detection means and the line-of-sight direction detected by the second detection means is less than a predetermined value, the line-of-sight direction detected by the first detection means is output as a detected direction and when the difference is greater than or equal to the predetermined value, the line-of-sight direction detected by the second detection means is output as a detected direction.
It is an object of the invention disclosed in Japanese Unexamined Patent Application Publication No. 2012-55428 to increase the reliability of the detection of a line-of-sight direction by using the line-of-sight direction detected by the second detection means when the first detection means cannot appropriately detect the cornea reflection image due to, for example, the influence of external light.
The gaze point detection method disclosed in International Publication No. 2012/020760 detects the cornea reflection point of a light source mainly on the basis of a dark pupil image. This cornea reflection point can be easily detected when the irradiation point irradiated with the light from the light source is located within the iris. However, when the inclination angle of the direction of a line of sight with respect to the optical axis of the light source becomes large, the irradiation point of the light is offset from the iris, whereby it becomes difficult to detect the cornea reflection point. Hence, detection based on the gaze point detection method is limited to the case in which the line-of-sight direction is within an angle range of about ±30 degrees with respect to the reference line described above, and in the case where the line-of-sight direction is deviated from the reference line by an angle larger than the above angle, the gaze point cannot be detected.
Japanese Unexamined Patent Application Publication No. 2012-55428 discloses the arrangement in which the line-of-sight direction is detected by using two detection means. However, the objective of using two detection means is to use a detected direction detected by the second detection means, thereby complementing the detection of the line-of-sight direction and enhancing reliability, when a cornea reflection image becomes undetectable in the first detection means due to, for example, external light. The objective is not to allow a line-of-sight direction to be detected even when the line of sight is considerably deviated from the front.
In view of the problems described above, the present invention provides a line-of-sight detection apparatus that can detect a line of sight over a wide angle by computing line-of-sight directions based on a plurality of portions of a face from the images of a face obtained by a camera, and by selecting one of a plurality of computed line-of-sight directions.